: The extraordinary potential of human embryonic stem cells (hESC) to differentiate into all cell lineages makes them attractive candidates to study developmental processes at the basic level, and also as candidates for cell or tissue replacement in regenerative medicine. Thus an in-depth understanding of their exact potential is imperative to move these fields forward as efficiently as possible. These lines all appear to be able to differentiate into derivatives of all three embryonic germ cell layers, however due to different culture conditions in the large numbers of laboratories using these cells, it is unclear exactly how similarly or differently these lines will behave when assessed for ability to differentiate under parallel conditions. Investigators in this Program Project have identified substantial differences in the abilities of several federally approved hESC to respond to identical differentiation-inducing signals. These signals were designed to differentiate hESC towards neuronal, germ cell and hematopoietic lineages, thus we see profound differences in differentiation of these cells along multiple lineages . The Program will be overseen and coordinated through the Administrative Core (Core A) and contains 3 research projects designed to optimize and characterize the differentiation of 4 federally approved hESC lines along these three lineages, and to assess potential epigenetic changes associated with differing differentiation profiles. These three projects will interact with the Stem Cell Core (Core B), which will provide hESC, optimize culturing of these cells as non-differentiated stem cells, and develop novel surfaces for hESC culture and differentiation. These Projects will also interact with the Epigenetic Core (Core C) and Computational and Bioinformatics Core (Core D), which will facilitate experiments on epigenetic control of gene expression. Each project will be independent, but will exchange data with each other, such that an epigenetic profile from undifferentiated hESC through differentiation towards all three lineages will be assembled. Thus we will employ continual comparison and feedback of differentiation results to determine whether the epigenetic signature of certain hESC lines results in improved yield or quality of some or all three lineages with differentiation. Taken together we will explore hESC differentiation potential and epigenetic control of differentiation along neuronal, germ cell, and hematopoietic lineages.